1. Field of the Invention
This invention relates to an image observation device which is handy to carry, and more particularly to an image observation device which can be held on the head or face of an observer.
2. Description of the Related Art
In the past, a conventional image observation device such as that set forth in Japanese Patent Preliminary Publication No. Sho 62-214782 has been known. FIG. 1 shows a conventional unit constructed so that a two-dimensional display element 21 is magnified and observed with an eyepiece 22, and supported in front of an eye 11 by supporting means not shown. FIG. 2 shows another conventional unit in which a plane mirror 24 is inserted between the two-dimensional display element 21 and the eyepiece 22 to bend its optical axis.
For the example depicted in FIG. 1, the two-dimensional display element 21 and the eyepiece 22 are arranged in a straight line. Thus, the device, when mounted on the head of the observer, protrudes a considerable amount from his face, giving rise to a situation which causes a disagreeable sensation to the observer. The weight of the entire device will be carried at the supporting point of his face or head and the considerable amount of protrusion of the device from his face increases the distance from the supporting point to the center of gravity in a horizontal direction, thus causing a great moment. Moreover, because the weight of the entire device is added to the supporting polar, the stability of the mounting is not secured, and there is a fear that the device may strike upon something when the observer walks or shakes his head.
In another example shown in FIG. 2, designed so that the optical axis Is bent, the entire device also considerably protrudes because of the plane mirror 24 obliquely placed as well as the thickness of the eyepiece 22. Furthermore, in this arrangement, when a virtual image is created to magnify and observe an image displayed on the two-dimensional display element 21 through the eyepiece 22, it is necessary to dispose the two-dimensional display element 21 closer to the eyepiece 22 than the object focal point of the eyepiece 22. As such, the insertion of the plane mirror 24 between the two-dimensional element 21 and the eyepiece 22 causes an increase of the optical distance between them, and hence the focal length of the eyepiece 22 must be increased accordingly. Furthermore, since the magnification of the eyepiece is inversely proportional to its focal length, this arrangement cannot bring about high magnification. It follows from this that the user observes a substantially small picture. As mentioned above, the two-dimensional display element itself has been observed directly through the eyepiece in the past to avoid mechanical interference with the plane mirror by the placement of the eyepiece. Consequently, the image observation device of the prior art has the defect that the magnification of the eyepiece cannot be increased.